1. Field of the Invention
The present invention relates to systems, methods and apparatus for the removal of volatile anesthetics from an anesthesia or ventilation system. In more particular, the present invention relates to a two-part or dual filter apparatus for removal of volatile anesthetics, the filter apparatus being adapted to be utilized with an anesthetic or ventilation system to facilitate the removal of inhaled or volatile anesthetics from the system intra-operatively or before the beginning of an anesthetic procedure to prevent or remedy a malignant hyperthermic response within a patient.
2. Relevant Technology
Malignant hyperthermia is a biochemical chain reaction response which can be triggered by commonly utilized inhaled anesthetics and the paralyzing agent succinylcholine within the skeletal muscles of susceptible individuals. The general signs of a malignant hyperthermia crisis include tachycardia, a greatly increased body metabolism, muscle rigidity and/or fever that may exceed 110 degrees Fahrenheit. Severe complications of malignant hyperthermia include, cardiac arrest, brain damage, internal bleeding or failure of other body systems. As a result, a secondary cardiovascular collapse resulting in the patient's death can occur if the patient's malignant hyperthermic reaction is not quickly identified and remedied by the practitioner.
Malignant hyperthermia susceptible persons have a mutation that results in the presence of abnormal proteins in the muscle cells of their body. Although normal in everyday life, when these patients are exposed to certain inhaled volatile anesthetic agents, it causes an abnormal release of calcium inside the muscle cell, which results in a sustained muscle contraction and the abnormal increase in energy utilization and heat production. The muscle cells eventually run out of energy, and die releasing large amounts of potassium into the bloodstream, which can lead to heart rhythm abnormalities. The muscle pigment myoglobin is also released which may be toxic to the patient's kidneys. Left untreated, these changes can cause cardiac arrest, kidney failure, blood coagulation problems, internal hemorrhage, brain injury, liver failure, and may be fatal.
The exact incidence of malignant hyperthermia is unknown. Some of the current medical literature estimates the rate of occurrence to be as frequent as one in 5,000 or as rare as one in 65,000 administrations of general anesthesia with triggering agents. The incidence varies depending on the concentration of malignant hyperthermia susceptible families in a given geographic area.
When a patient unexpectedly experiences a malignant hyperthermia reaction, after the patient is anesthetized and the surgery has begun, different protocols are utilized to treat the patient. In this case, it is necessary to turn off the anesthetic vaporizer, increase the fresh gas flow to flush the vapor for the breathing circuit and increase patient ventilation. The actions of turning off the anesthesia vaporizer and increasing fresh gas flow decrease the amount of vapor that is re-circulated to the patient, but they do not eliminate it. During the first minutes after the anesthesia vaporizer has been turned off, the patient continues to exhale a significant volume of anesthetic vapor. Due to the closed loop configuration of many anesthesia delivery machines, some of this previously exhaled vapor is inevitably re-inhaled.
The other situation in which malignant hyperthermia will be addressed by a practitioner is in the preparation of an anesthesia machine for use in a patient that is known, or suspected, to be susceptible to malignant hyperthermia. In this situation, the exigencies of the medical procedure can necessitate the use all of the capabilities of the anesthesia machine including ventilation, monitoring, oxygen delivery, etc. with the notable exception that delivery of volatile anesthetic vapor will not be utilized. When an anesthesia machine is to be utilized with a patient that is susceptible to malignant hyperthermia, residual anesthetic vapor must be thoroughly scrubbed from the machine until the residual vapor concentration in the gas delivered by the machine to the patient is below the suggested limit of 5 parts per million. Because some of the parts in newer anesthesia machines are made of plastic materials that tend to retain anesthetic gases, clearing the anesthetic gases completely from the machine can take hours. In fact, many hospitals have protocols that require the machine to be flushed for multiple hours before use in these patients, or require that a “clean” machine that has been in storage be used in malignant hyperthermia susceptible patents. As will be appreciated, not only is the use of such protocols time consuming, but the anesthesia machine is unable to be utilized in other anesthesia procedures during this time, resulting in increased costs and inefficiency in use of the hospitals capital equipment.
It has been shown that placing a charcoal filter on the inspired limb of the anesthesia machine effectively removes the residual anesthetic so that the machine can be used immediately. However, there is a risk that the filter be placed incorrectly on the expired limb of the anesthesia circuit. Additionally, the use of a single thick filter needed to adsorb inhaled anesthetics can result in undesirable increase in back pressure limiting the ease of gas delivery to the patient. Finally, placement of a single filter on the inspired limb does not address the reintroduction of inhaled anesthetics back to the system from patients who have already been administered such anesthetics. Furthermore, using only a single filter does not preclude the accidental placement of the filter on the incorrect limb of the anesthesia or ventilator system.